Combined Chemical Oxidation/Assisted Bioremediation of Contaminats

ABSTRACT

Particles containing a metal peroxide in which the metal is chosen from the groups IIa and IIb of the periodic table and in which at least 50% by weight of the particles have a diameter higher than 20 μm. Process for the preparation of such particles comprising: (a) mixing at least one metal oxide or hydroxide, the metal being chosen from the groups IIa and IIb of the periodic table, in the form of an aqueous solution, a suspension or a solid, with an aqueous hydrogen peroxide solution, (b) allowing the metal oxide or hydroxide to react with hydrogen peroxide to form a suspension of the corresponding peroxide, (c) adding to this suspension at least one additive, and (d) drying the resulting peroxide suspension.

FIELD OF THE INVENTION

The invention relates in general to compositions and methods forcleaning contaminated materials such as soil and water.

Additional advantages and other features of the present invention willbe set forth in part in the description that follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from the practice of thepresent invention. The advantages of the present invention may berealized and obtained as particularly pointed out in the appendedclaims. As will be realized, the present invention is capable of otherand different embodiments, and its several details are capable ofmodifications in various obvious respects, all without departing fromthe present invention. The description is to be regarded as illustrativein nature, and not as restrictive.

SUMMARY OF THE INVENTION

The invention objectives are accomplished, in general, by the combineduse of metal (e.g., Fe) chelates, especially transition metal chelates,and a source of peroxide, especially Mg, Ca, and/or Zn peroxide orsodium percarbonate (PCS) or hydrogen peroxide. An underlying concept isthe reaction of hydrogen peroxide which is used as such or which isgenerated from, e.g., PCS or CaO₂, with a metal chelate. One advantageof a metal chelate is that it is kept in solution under alkalineconditions allowing the H₂O₂ to react with the metal generating amodified Fenton process thereby producing hydroxyl free radicals whichare very strong oxidants that degrade contaminants.

BACKGROUND OF THE INVENTION

The strongest oxidizing agent suitable for soil and groundwaterremediation is the hydroxyl free radical. The typical way to generate OHradicals is through the Fenton system using H₂O₂ and ferrous ions at pH3-4. Hydroxyl free radicals can also be generated by the use of acombination of ozone and H₂O₂ or UV and H₂O₂.

While these technologies are effective, they suffer from some drawbacks:

-   -   Fenton technology is only suitable at a low pH, hence the need        to acidify which requires the use of stainless steel piping and        is expensive.    -   Ozone/H₂O₂ technology requires on site generation of ozone and        can be expensive.    -   UV/H₂O₂ technology is not suitable for in-situ remediation.

Hydrogen peroxide solutions are available in several concentrations. Thetypical concentration used in soil remediation is the 35% grade. This isfurther diluted to lower concentrations for example 5-12%, beforeintroduction in the contaminated material to be treated.

Sodium percarbonate (PCS) is a peroxyhydrate composed of sodiumcarbonate and H₂O₂. Its solubility in water is ˜12%. Upon dissolution inwater, it releases its components and the resulting solution containsboth soda ash and H₂O₂.

Calcium and magnesium peroxide are solid peroxygens that are insolublein water. When they are mixed with water, they slowly release oxygen attheir natural pH (>pH 10). They are used in soil and groundwaterremediation to provide oxygen to aerobic bacteria thereby enhancingtheir capability of degrading various contaminants.

As the pH is lowered, CaO₂ and MgO₂ generate increasingly largerquantities of H₂O₂. For example, at a pH 8, approximately 60% of theactive content of CaO₂ can be generated in the form of H₂O₂.

Whereas OH radicals can be generated at any pH due to H₂O₂decomposition, the optimal use of this process for chemical oxidationoccurs at a pH of 3-4 whereby the Fe ions remain soluble, and cyclebetween a ferrous and a ferric state.

U.S. Pat. No. 6,268,205 discusses the use of inorganic peroxides inconjunction with buffers and catalyst such as ferrous or ferric sulfate.The pH of such system is adjusted to 7-9. Under these conditions, themetal peroxides will release their activity partially as H₂O₂ andpartially as oxygen. This allows for the initial chemical oxidation totake place starting the break up of the contaminants. The oxygen is thenreleased more slowly, which will assist bioremediation over a period ofseveral months. Although OH radicals can be generated from H₂O₂ at thispH, Fe will precipitate as ferric hydroxide. The net result is a reducedgeneration of OH radicals and clogging of the medium with theprecipitated ferric hydroxide.

U.S. Pat. Nos. 5,741,427 and 6,319,328 are related to the use of Fesalts or chelates that are dissolved in water, the solution ismaintained at pH 5-8, and then injected to a soil that has already beeninjected with an oxidizing agent. This pH is lower than the pH claimedin the above patent and would lead to a very fast release of H₂O₂ fromthe solid peroxides. The order of addition claimed results in a reducedactivation of H₂O₂ as the peroxide would be partially decomposed priorto the injection of the metal chelate.

U.S. Pat. No. 6,843,618 is related to a method of decontaminating soiland ground water containing organic contaminants and divalent metalcompounds. It comprises the steps of first treating such soils andground water with an effective amount of an aqueous solution containinga peroxide and a water soluble chelating agent for a time sufficient tohave the water soluble chelating agent chelate at least one of thedivalent metals of the divalent metal compounds present in the soil andground water. Next, the chelated metals are brought into contact withthe peroxide to catalytically convert the peroxide to an oxidizingagent. Finally, the last step is contacting the organic contaminants inthe soil and ground water with the oxidizing agent to oxidize theorganic contaminants to environmentally safe, non-toxic compounds.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The invention is related to a kit for the combined chemicaloxidation/assisted bioremediation of contaminated materials, comprising:

i. at least one metal chelate, and

ii. at least one peroxide compound.

The term “assisted bioremediation” is intended to denote enhancing thegrowth of aerobic microorganisms by supplying them with oxygen, therebyallowing them to multiply faster leading to an increased rate ofdegradation of the contaminants.

The “at least one metal chelate” comprises preferably a transition metalchelate such as Fe chelate.

The “at least one peroxide compound” comprises is most cases aninorganic peroxide. It comprises preferably at least one of Ca, Mg andZn peroxide or sodium percarbonate or hydrogen peroxide. In some casesit is recommended that the kit comprises at least two different peroxidecompounds. One of the two peroxides is most often chosen from sodiumpercarbonate and hydrogen peroxide. The other peroxide is in many caseschosen from Ca, Mg and Zn peroxides. Preferred combinations of twodifferent inorganic peroxides include one of H₂O₂ and sodiumpercarbonate, and one of Ca, Mg and Zn peroxides (especially CaO₂.),most preferably sodium percarbonate and one of Ca, Mg and Zn peroxides(especially CaO₂). The combination of one of H₂O₂ and sodiumpercarbonate and CaO₂ gives good results.

The invention is also related to a method for the combined chemicaloxidation/assisted bioremediation of contaminated materials, comprisingcontacting a contaminated material with at least one metal chelate andat least one peroxide compound.

The contaminated material is in most cases soil or water. The metalchelate and the peroxide compound are as described above.

According to the method of the present invention, the metal chelate canbe added to the contaminant/medium and/or a chelating agent can be addedto a medium that already contains a transition metal such as Fe wherebythe metal chelate forms in situ.

When at least two different peroxide compounds are used, the inventioncomponents (metal chelate and the two peroxides) can be added in anyorder. In some cases, it can be advantageous to add first the metalchelate and then in a later stage the two peroxides together orsequentially. In other cases, a peroxide compound, preferably one of Ca,Mg and Zn peroxides, is added in a first stage; then in a second stagethe metal chelate is added and in a third stage, the second peroxidecompound, preferably sodium percarbonate or hydrogen peroxide, is added.In any way, when sodium percarbonate or hydrogen peroxide are used, itis recommended to add the metal chelate before or together with thesodium percarbonate or hydrogen peroxide, preferably before. In othercases, the metal chelate is first added to the contaminated material ina first stage, then in a second stage the first peroxide compound isadded, preferably sodium percarbonate or H₂O₂, and then the secondperoxide compound is added preferably one of Ca, Mg, and Zn peroxides.

A preferred embodiment of the invention includes the use of at least onemetal chelate, especially transition metal chelate, such as a Fechelate, either as such, or in the form of the metal salt (e.g., ferrousor ferric salt) and a separate ligand (all of which are hereinafterreferred to as “metal chelate”). The metal chelate can either be addedtogether with all other components of a peroxide solution or slurry, orseparate injections or additions to the material being treated may bemade whereby the peroxide solution or slurry is added either before,during or after the metal chelate. Alternatively, the chelating agentmay be added to the material being treated (e.g., soil) in order tochelate with metals such as Fe in the ground. A buffer can be also addedeither in the peroxide solution or slurry, or with the metal chelate toadjust the pH, preferably to 7-9. Preferred transition metals other thanFe include Mn and Cu, and are in particular those capable of generatingOH radicals from H₂O₂. Optionally, products that are considerednutrients to microbes can also be added either separately or incombination with other products in a solution or slurry. As appropriate,some products may be injected or mixed in their dry form. Metal chelatesdescribed in U.S. Pat. No. 5,741,427 and U.S. Pat. No. 6,319,328 can beused herein. A preferred metal is Fe. Preferred chelating agents(ligands) include EDTA, citric acid, nitrilotriacetic acid, EDTA acidtypes, diethylenetriaminepentaacetic acid,hydroxyethylenediaminetriacetic acid, methylglycinediacetic acid,phosphonates, and the TRILON® chelating agents of BASF, the brochure forwhich is incorporated herein by reference.

One objective of the invention is to create a dual acting system forcatalytic oxidation of contaminated materials in soil and groundwaterusing oxidizing products in combination with a chelated metal catalyst(e.g., transition metal) as well as the generation of oxygen forassisted bioremediation. The chelating agent can be mixed in with themetallic catalyst or applied separately if sufficient amounts of themetallic catalyst already exist in the material to be treated.

In a preferred embodiment, the chelating agent should be added first, toallow for its reaction with the metals of the water, soil, etc. Thechelating agent may for example be dosed at a level of 0.01-0.5% of,e.g., sodium percarbonate by moles. One suggested application rate is0.1%. If a metal chelated complex is used, this can be of any transitionmetal but in particular of iron, manganese and copper, and is preferablyadded first.

The soil contaminants that can be effectively treated includepetrochemicals, chlorinated organics, pesticides, energetics,perchlorates, etc.

Application can be accomplished in any manner, for example byintroducing the solid, solution, or suspension in the material to betreated in any manner known in the art. Alternatively the peroxide(e.g., sodium percarbonate (PCS)) can be dissolved and introduced as asolution.

All components mentioned herein may be used as mixtures of such.

The relative amounts of invention compounds are not limited. Preferably,the mole ratio of metal chelate to peroxide is 0.01-10 metalchelate/peroxide, more preferably less than 1, for example 0.05, 0.1,0.2, 0.3, etc. With regard to treatment, the amount of inventioncomponents applied to the material being treated is not limited, and canrange for example from a ratio of for example 0.0001 to 10,000(invention components in pounds (lbs)/cubic feet of material beingtreated). A generally useful range is 0.01-1.5, for example 0.2-1. Apreferred range of dosing is up to 2,000 mg/L.

The source of peroxide may be any known in the art, for example any oneor combination of CaO₂, MgO₂, PCS and/or H₂O₂. Preferred are CaO₂ andone of PCS or H₂O₂. While not bound by any theory, it is believed thatthe addition of H₂O₂ or PCS results in the immediate presence of H₂O₂,which quickly starts the oxidation reaction. The reaction then continuesas a result of the slow release of H₂O₂ from the other sources, such asCaO₂ and/or MgO₂. The latter two products also generate oxygen for longterm assisted bioremediation.

The peroxide compound (such as CaO₂) is typically added as a slurry. Twoexamples of typical concentrations are for instance about 20% by weightand about 35% by weight. The slurry could be more dilute if the materialbeing treated is very porous.

Alternatively, the peroxide compound can be added as solid particles.They could be used in the soil remediation application as a solid mixedwith the soil or as a solid mixed with another invention component. Thesolid particles can be used in the form of a powder or as granules.Granules of inorganic peroxides are described in the European patentapplication of SOLVAY filed under the number EP 05104226.5 on 19 May2005, the content of which is incorporated herein by reference.

When the peroxide compound is sodium percarbonate, it can be used in theform of a solution or a suspension. Concentrations can be for example 8%by weight in the case of a solution and for example 20% by weight in thecase of a suspension. A particularly suitable sodium percarbonateproduct has particles with a mean particle size in the range of from100, to 400 μm. A 100 μm product may offer advantages in handlingbecause it is a finer material compared to classical products. It iseasier to dissolve and pumping its suspension is also easier. Sodiumpercarbonate can also be mixed with the soil in a solid form either bysimple mixing or by incorporation with the machine that is excavatingthe soil during excavation.

The metal chelate is typically added in the form of a solution. Thesolution concentration can be for example 4% by weight. The metalchelate can be prepared ex situ, for instance in the case of a Fechelate it can be prepared ex situ by mixing an iron salt such as FeSO4with the chelating agent solution. One way to do this consists in mixing0.9 kg Fe salt with 7.6 L of 40% chelating agent solution (3 kg ofchelant (100%)), and by diluting this solution four fold.

The combined chemical oxidation/assisted bioremediation treatmentaccording to the invention can further be combined with any othersuitable treatment.

This invention has advantages over U.S. Pat. No. 6,268,205 in that themetal chelate has a greater ability to catalyze the chemical oxidationas, e.g., Fe hydroxide would not precipitate. This approach is alsobetter than U.S. Pat. Nos. 5,741,427 and 6,319,328 in that the higher pHwill allow for the slow release of oxygen over a greater period of time,thus assisting the naturally occurring microbes in degrading thecontaminant.

The current invention also has advantages over U.S. Pat. No. 6,843,618in that it allows for both chemical oxidation and assistedbioremediation of contaminants. Further, the chemical oxidation canoccur in two stages encompassing an immediate oxidation followed by anextended reaction due to the slow release of H₂O₂ and oxygen from theCaO₂ or MgO₂ or ZnO₂. This invention also allows for the addition of thevarious components in any suitable sequence which improves theeffectiveness of treatment.

The above written description of the invention provides a manner andprocess of making and using it such that any person skilled in this artis enabled to make and use the same, this enablement being provided inparticular for the subject matter of the appended claims, which make upa part of the original description.

All references, patents, applications, tests, standards, documents,publications, brochures, texts, articles, etc. mentioned herein areincorporated herein by reference. Where a numerical limit or range isstated, all values and subranges therewithin are specifically includedas if explicitly written out.

The above description is presented to enable a person skilled in the artto make and use the invention, and is provided in the context of aparticular application and its requirements. Various modifications tothe preferred embodiments will be readily apparent to those skilled inthe art, and the generic principles defined herein may be applied toother embodiments and applications without departing from the spirit andscope of the invention. Thus, this invention is not intended to belimited to the embodiments shown, but is to be accorded the widest scopeconsistent with the principles and features disclosed herein.

EXAMPLE 1

Soil and groundwater at a former fuel distribution demonstration sitewere contaminated with petroleum hydrocarbon from 19 former undergroundstorage tanks (USTs) over the one acre property. Depth to groundwater(DTW) in the primary source treatment area was approximately 16 feetbelow ground surface (ft bgs) and ranged as deep as 22 ft bgs over theremainder of the plume. The aquifer primarily consisted of clayey sandwith low levels of naturally occurring organic carbon. Soilcontamination primarily existed from the base of the UST excavationdepth of approximately 13 ft bgs and into the groundwater. The excavatedUST pits were primarily backfilled with soft sedimentary rock allowinghigh infiltration rates during precipitation events. The soil has highin iron content.

Free-phase petroleum 0.04 to 0.07 ft thick was consistently detected inthe two wells located in the primary source area prior to treatment.However, source area dissolved phase concentrations were low due eitherto continued influx of uncontaminated groundwater or because thecontaminants were highly adsorbed in the soil with very little productextractable from the dissolved phase. Contaminant concentrationsdowngradient indicate that low concentrations are likely the result offresh influx of groundwater.

The existence of free-phase hydrocarbons warranted a dual stage remedialapproach including chemical oxidation and bioremediation treatment.Chemical oxidation with sodium percarbonate was initiated to quicklyreduce sorbed phase and free phase petroleum constituents, as well assupply an oxygen boost to the aquifer. Calcium peroxide was appliedconcurrently to provide a slow release source of hydrogen peroxide aswell as oxygen for enhancing aerobic microbial growth. In the presenceof high concentrations of contaminants, it is difficult to supply enoughoxygen to sustain aerobic microbial growth and resultant contaminantdegradation. Application of calcium peroxide alone for the purpose ofenhancing bioremediation would not be effective on high contaminant orfree-phase concentrations. The dual stage approach was initiated only inthe primary source area, the majority of the site was treated withcalcium peroxide alone.

The dual stage application is the topic of this example. The source areainjection grid was designed on approximately 5 foot centers to promotecontact of contaminants with high concentration of the chemicals.Treatment was applied to the superficial ten feet of groundwater and onefoot of unsaturated soils immediately above the groundwater table byinjecting chemicals in the form of a suspension or solution through theone-inch rods of a Geoprobe Model 6600 geoprobe direct push truckmounted rig.

The chemicals were applied as follows in each injection:

-   -   First a suspension of calcium peroxide in water was injected at        a depth of 19-26 ft bgs. The suspension was ˜28% prepared using        75 lbs calcium peroxide suspended in 120 gallons of water.    -   The soil contained a high Fe content, therefore a chelating        agent was added and allowed to react with Fe in the soil in        order to produce the Fe chelate. The chelating agent was        immediately injected after the injection of the calcium peroxide        slurry and in a similar manner at a depth of 15-19 ft bgs.        Approximately 8 gallons of Trilon M solution (39-41%        methylglycinediacetic acid—MGDA-Na₃) were diluted with water in        a ratio of 1:10 chelant to water.    -   After a period of 2-4 hours, the sodium percarbonate was        injected at a depth of 15-19 ft bgs. The aqueous        solution/suspension had a concentration of 8-12% and about 75        lbs sodium percarbonate were used.

The hydraulic conductivity of the formation was great enough thatsignificant back pressure did not occur during injection.

A second injection was made after 23 weeks without adding the chelatingagent as it was considered that the Fe chelate formed after the firstinjection was still present in the soil.

Groundwater samples from site wells located within and outside of thecontaminant plume were collected for laboratory analyses 7 weeks priorto the initial treatment and 13, 23, and 40 weeks after the initialinjection. Field physicochemical measurements have been collectedmonthly following the initial injection.

Results

During the initial injection of sodium percarbonate, a brown foam wasobserved at the surface resulting from the reaction of the oxidant andpetroleum contaminated groundwater. This resulted in the elimination ofthe free-phase contaminants. It is assumed a similar reaction occurredthroughout the contaminated zone in the subsurface. The low levels ofnaturally occurring organic carbon allowed the reaction to occurprimarily upon the contaminants.

The following tables show the effect of treatment. In summary

-   -   Disappearance of the free product at the source area where the        injection was made, with a drop from ˜0.07 ft to no detection        after 32 weeks.    -   BTEX (benzene, toluene, ethylbenzene, xylenes) and naphthalene        concentration.        -   In the source area, these contaminants were adsorbed onto            the soil and could not be detected in the aqueous phase.            Upon treatment, their levels first increased in the aqueous            phase through desorption and then dropped in concentration            over the period of the treatment.        -   A downgradient well that had a large concentration of these            contaminants showed a decrease in contaminants level over            the treatment period. After 40 weeks, some rebound was            observed likely due to the consumption of the peroxide            compounds, requiring a re-injection.    -   Specific conductance is an indication of dissolved organics. The        higher the value, the greater the dissolved organics. Specific        conductance dropped after treatment but rebounded later        indicating an additional amendment application is needed to        continue product degradation.    -   Oxidation Reduction Potential (ORP) is an indication of the        oxidizing potential of the medium. In a completely treated soil,        this value should be positive. In this case, due to the very        high contamination, the value remained negative throughout the        treatment but slowly increased.        -   Source area: increased from −162 to −16 mV after 40 weeks.        -   Immediately downgradient: increased from −153 to +332 mV but            dropped later to −2 mV after 40 weeks.

Overall, the treatment has been highly successful at eliminating thefree-phase hydrocarbons in the primary source area. A third dual stageapplication is planned to reduce the sorbed phase petroleum hydrocarbonsin the unsaturated zone above the treatment area. Weeks since TreatmentSource Area (MW-7) 7 weeks before treatment 4 9 13 17 23 32 40 Benzene -μg/L nd 80 42 16 Toluene - μg/L nd 35 nd 6.0 Ethylbenzene - μg/L nd 3709 67 Xylenes (total) - μg/L nd 750 19 160 MTBE - μg/L nd nd nd ndIsopropylbenzene (cumene) - nd 36 nd nd μg/L Naphthalene - μg/L 11 110 719 Free product sheen - ft 0.07 0.04 0.04 0.01 0.02 0.02 0.00 0.00Specific conductance - ohms na 2,108 1,620 937 1,117 1,030 1,345 1,525ORP - mV na −162 −180 −163 −138 −136 −108 −16 pH na 6.3 5.7 6.0 6.2 6.56.5 6.5nd = non detectedna = not available (not measured)

Weeks since Treatment Immediately downgradient MW-6 7 weeks beforetreatment 4 9 13 17 23 32 40 Benzene - μg/L 2,300 49 67 850 Toluene -μg/L 23 nd nd 8 Ethylbenzene - μg/L 40 nd nd 26 Xylenes (total) - μg/L1,000 33 31 250 MTBE - μg/L 25 nd nd 8 Isopropylbenzene (cumene) - μg/L45 nd nd 14 Naphthalene - μg/L 29 nd nd nd Free product sheen - ft — — —— — — — — Specific conductance - ohms 2,050 1,160 824 651 779 608 1,4582,418 ORP - mV −153 −24 311 332 3 163 −41 −2 pH 6.5 6.1 6.0 6.0 6.4 6.46.1 6.6

EXAMPLE 2

Another site was contaminated with Diesel Range Organics (DRO) andpetroleum hydrocarbons. The water table was high in this site as it islocated next to a river. The depth to the groundwater (DTW) was about 14ft.

Application

Due to the low iron at this site a ferrous chelate was formed ex-situprior to injection.

The injections were done as follows:

-   1. Two pounds of ferrous sulfate were mixed with 2 gallons of    chelant (Trilon M). Several hours later, the solution was diluted    with water at a volume ratio of 1:4 chelate:water.-   2. The solution was equally applied in 16 wells as the Geoprobe rods    were advanced through the water table.-   3. As the rods were pulled out of the hole, a sodium percarbonate    slurry was pumped at a concentration of 20%. About 47 lbs sodium    percarbonate were injected in each well (750 lbs sodium percarbonate    were used for the 16 holes).-   4. This was followed by injecting a 20% calcium peroxide slurry.    About 17 lbs of calcium peroxide were injected in each well (275    pounds CaO₂ suspended in 160 gallons of water for the 16 holes).    This material was also applied from the bottom up.

The 16 injection points were installed in a circle around the monitoringwell, with 8 located at 5 feet from the monitoring well, and the other 8located at a distance of 10 feet from the monitoring well.

Results

A few wells showed a dramatic increase in dissolved oxygen shortly afterinjection. 5 days before Days from Treatment Centre Area (MW-23)treatment 1 7 30 Specific conductance - ohms 568 533 546 657 ORP - mV−109.6 247 127 126 Dissolved oxygen conc. - mg/L 1.48 1.17 1.49 2.29 pH7.13 7.01 7.16 8.29

1: A kit for the combined chemical oxidation/assisted bioremediation ofcontaminated materials, comprising: i. at least one metal chelate, andii. at least one peroxide compound. 2: The kit according to claim 1,wherein said at least one metal chelate comprises a Fe chelate. 3: Thekit according to claim 1, wherein said at least one peroxide compoundcomprises at least one of Ca, Mg and Zn peroxide or sodium percarbonateor hydrogen peroxide. 4: The kit according to claim 1 comprising atleast two peroxide compounds. 5: The kit according to claim 4 comprisingone of hydrogen peroxide or sodium percarbonate and one of Ca, Mg and Znperoxide. 6: A method for the combined chemical oxidation/assistedbioremediation of contaminated materials, comprising contacting acontaminated material with at least one metal chelate and at least oneperoxide compound. 7: The method according to claim 6, wherein saidmaterial is soil or water. 8: The method according to claim 6, whereinsaid at least one metal chelate comprises a Fe chelate. 9: The methodaccording to claim 6, wherein said at least one peroxide compoundcomprises at least one of Ca, Mg and Zn peroxide or sodium percarbonateor hydrogen peroxide. 10: The method of claim 4, wherein the metalchelate can be added to the contaminant/medium and/or a chelating agentcan be added to a medium that already contains a transition metalwhereby the metal chelate forms in situ. 11: The method according toclaim 6, wherein a buffer is added to adjust the pH to a value of from 7to
 9. 12: The method according to claim 6 wherein at least two peroxidecompounds are used, the metal chelate and the at least two peroxidecompounds are added in any order. 13: The method according to claim 12wherein one of hydrogen peroxide and sodium percarbonate and one of Ca,Mg and Zn peroxide are used. 14: The method according to claim 13,wherein the one of Ca, Mg and Zn peroxide is added in a first stage, themetal chelate is added in a second stage, and the one of sodiumpercarbonate and hydrogen peroxide is added in a third stage. 15: Themethod according to claim 13, wherein the metal chelate is added in afirst stage, the one of hydrogen peroxide and sodium percarbonate isadded in a second stage, and the one of Ca, Mg and Zn peroxide is addedin a third stage. 16: The method according to claim 13, wherein themetal chelate is added in a first stage, the one of Ca, Mg and Znperoxide is added in a second stage and the one of hydrogen peroxide andsodium percarbonate is added in a third stage.